High-power narrowed-linewidth fiber laser system

Abstract

A high-power narrow-linewidth fiber laser system includes a seed oscillator with multiple resonant cavities and an amplifier stage. The seed oscillator includes a gain fiber, a pump source to introduce pump light into the gain fiber, a single-mode output fiber arranged at the end of the active gain fiber, a first resonant cavity including the active gain fiber, and a second resonant cavity including the active gain fiber. The first and second resonant cavities cooperate to minimize the synchronization of longitudinal modes and thereby reduce modal beating. The amplifier preferably includes an active multimode gain fiber capable of supporting a single fundamental mode at the signal wavelength, wherein the single mode output fiber of the seed oscillator and the multimode gain fiber of the amplifier are mode-matched and coupled without a mode converter.

1. A fiber laser system operative to emit a light signal within a predetermined narrow linewidth, the fiber laser system comprising:
 an active fiber; 
 a plurality of upstream passive fibers having respective inner ends operatively connected to one of opposite ends of the active fiber; 
 an output passive fiber having an upstream end, which is coupled to an other end of the active fiber, and a downstream end outputting the light signal; 
 multiple strong reflectors in respective upstream fibers and a weak reflector in the output fiber, the strong reflectors and the weak reflector defining respective resonators therebetween of different lengths each supporting longitudinal modes of the light signal, the longitudinal modes circulating in respective resonators being combined together so that the longitudinal modes of one resonator are spectrally offset from those of an other resonator, wherein the intensity of mode beating among the combined longitudinal modes is minimized. 
 
     
     
       2. The fiber laser system of  claim 1 , wherein the plurality of strong reflectors each are a fiber loop mirror, the weak reflector being a Bragg grating. 
     
     
       3. The fiber laser system of  claim 1  further comprising a coupler providing an interface between the inner ends of the upstream passive fibers and the one end of the active fiber. 
     
     
       4. The fiber laser system of  claim 2 , wherein the weak reflector includes a tunable fiber Brag grating. 
     
     
       5. The fiber laser system of  claim 1 , wherein the plurality of upstream passive fibers, active fiber and output passive fiber define an oscillator. 
     
     
       6. The fiber laser system of  claim 5  further comprising at least one fiber amplifier configured with an active fiber and upstream and output passive fibers which are operatively connected to respective ends of the active fiber of the fiber amplifier, the upstream passive fiber of the amplifier and output passive fiber of the oscillator being operatively connected to one another so that the light signal is coupled into the upstream passive fiber of the amplifier without losses. 
     
     
       7. The fiber laser system of  claim 6  further comprising a plurality of pump source each configured to introduce pump light into the active fiber. 
     
     
       8. The fiber laser system of  claim 6 , wherein the passive and active fibers are configured with substantially identical mode filed diameters to minimize losses of the light signal. 
     
     
       9. The fiber laser of  claim 6 , wherein the upstream and output passive fibers of the respective oscillator and amplifier are single mode fibers.